The production of compressed, shaped articles designated as “composites” from small wood pieces, wood fibers or wood particles, such as, for example, OSB boards (oriented strand board), particleboards, fiberboards or plywood, but also cork boards and moldings comprising flax, straw and other cellulose-containing materials using isocyanate binders, optionally in the presence or absence of catalysts, auxiliaries and/or additives in an open or closed mold is known from numerous patent and literature publications.
In these processes, temperatures of from 90° to 270° C. are necessary in order to ensure the reaction of the isocyanate binder with the cellulose-containing material and to permit molding of the materials to give the desired final shape, such as, for example, boards or sheets.
Although the production of compact cellulose/isocyanate moldings has become very important industrially, the processes described in the prior art also have technical deficiencies, for example owing to the outstanding adhesion of polyurethanes to other materials. A particular disadvantage in the prior art processes is that the moldings adhere to the molds and are therefore difficult to remove from the mold, which frequently leads to damage to the molding, in particular the surface thereof. In order to avoid this disadvantage, as a rule, polished metallic molds are used and/or release agents are concomitantly used.
These mold release agents are either used as internal lubricants in the curable cellulose-isocyanate mixture, or the inner surfaces of the mold are provided with a uniform coating of external lubricants before the production of the moldings. Various injection and spraying and roll application methods (DE-10 337 594) are known for this purpose in the prior art. It is also possible to coat the surface of the wood strands with a mold release agent. This is also effected by application by spraying.
Conventional internal or external lubricants used are, for example, fatty acids and the metal salts thereof (WO-A-03/072324, WO-A-02/36268), polymeric fatty acids (EP-A-0 269 869), carboxy-functionalized siloxanes (EP-B-0 129 430), waxes (EP-B-0 046 014) especially ester wax (EP-B-0 057 502), oxidized wax (WO-A-00/53381) or polyolefin wax (WO-A-98/00464), polyolefin wax in combination with fatty acids (WO-A-01/58998) or finally fatty acids or wax acids in combination with polysiloxanes, which are modified with an organically bonded active hydrogen group and are capable of reacting with isocyanate (WO-A-03/008164).
Such conventional release agents have the disadvantage that the surface of prepared moldings show dark discoloration, which greatly impairs the optical value. Furthermore, the press plates frequently exhibit black accumulated residues. This is because the conventionally used release agents are not thermally stable or stable to oxidation at the temperatures used in the process and/or tend to produce hard, generally black solid accumulated residues on the metal plates.
These accumulated residues can, in turn, also be deposited on the moldings produced and, in this way, also lead to dark discolorations and/or irregularities in the surface structure thereof or, particularly in the case of silicone-containing release agents, lead to considerable coating problems. In some cases, an after-treatment such as grinding of the surface is necessitated thereby.
The release agents currently used industrially for demolding of shaped articles usually contain substances dispersed in a carrier and having release properties.
Carriers used are, as a rule, organic solvents or water. They serve not only as carriers for the materials having release properties and as solvents for further additives, but also for establishing an optimum concentration, as auxiliaries for wetting and leveling and in the formation of the release agent film and for influencing the surface of the shaped polyurethane article. Operational safety, cost efficiency and ecological safety are further requirements which the carrier has to meet.
The greatly increased interest in environmental protection and the more stringent legal provisions associated therewith lead to efforts to reduce volatile organic solvents (so-called VOCs) to an acceptable minimum.
The release agents currently used industrially for demolding of shaped articles usually contain substances dispersed in a carrier and having release properties, such as, oils, waxes, silicones and/or soaps.
EP-A-0 207 192 describes silicone resins as semipermanent release agents for the press plates, which cure on the press plates and permit repeated demolding. This reference mentions amino-functionalized siloxanes in combination with silicone resins. Additional, this reference indicates that the release agent should acquire a certain compatability with the resin matrix, which ensures incorporation into the matrix. The problems already described and relating to the formation of dark accumulated residues on the press plates are, however, not eliminated by this prior art release agent.
DE-C-19 738 192 describes release agents for molds for the production of moldings from plastics composed of volatile polysiloxanes having chain lengths of 7 to 13, in which from 0.1 to 5.0% by weight of a polysiloxane containing γ-aminopropyl groups is concomitantly used. The release agent is used at room temperature, or temperatures of up to 50° C. However, these release agents cannot be used for the present application since the volatile polysiloxanes can no longer act as release agents at high application temperatures from 180° to 270° C. and/or do not permit the formation of a uniform release agent film on the press plates. Furthermore, it was to be feared that discolorations occur with the use of polysiloxanes containing amine groups.